Production of filaments



' like.

Patented June 9, 1942 UNITED STATES PATENT. OFFICE rnonuc'rrou orFILAMENTS Johannes All-than, New York, N. Y., assignor to E. I. du Pontde Nemours & Company, Wilmington, Del., a corporation of Delaware NoDrawing.

Application July 25, 1940,

Serial No. 347,492

Claims.

This invention relates to the production of filaments of syntheticlinear condensation 1937 now Patent No. 2,130,948, all of w. H.

Carothers. These polymers are capable of being formed by melt-spinninginto filaments, ribbons, and the like, which possess the unusualproperty of being capable of being cold-drawn," i. e., drawn orelongated under application of stress in the solid state, with resultingorientation of internal structure and corresponding marked benefits totheir mechanical properties.

In a copending application for United States Patent filed by G. D.Graves on February 15, 1937. entitled Synthetic polymers and shapedarticles therefrom, Serial No. 125,926, now Patent No. 2,212.772 isdisclosed and claimed a step, conveniently designated quenching, whichimproves very materially the strength, toughness. and pliability offilaments and the like thus spun and drawn. The step of quenchingcomprises essentially bringing the filaments and the like, immediatelyupon their formation from molten polymer, into contact with anon-solvent liquid maintained at such temperature as to effect. rapidchilling of the filament and the The procedure disclosed in this Gravesapplication is broadly applicable to synthetic linear condensationpolymers and contemplates the use of a quenching liquid maintained at atemperature within a wide range although favoring a temperature somewhatbelow ordinary temperature to insure a wide difference between thetemperature of the freshly spun polymer and the quenching liquid.

In certain uses of filaments of synthetic linear condensation polymers,particularly to coarser filaments, it is of great importance that thefilament be substantially perfectly circular in cross section and it is,therefore, important to produce such filament with a minimum ofdeviation in cross sectional shape from that of the circular orificefrom which it has been spun. With some of these polymers, it appearsthat the production of filaments of circular cross section may readilybe accomplished by following the teachings of the prior art but this hasnot been the case with respect to filaments of polymeric hexamethyleneadipamide.

An object of the present invention is to provide a process ofmanufacturing polymeric hexamethylene adipamide filaments which aresubstantially perfectly circular in cross section. A further object isto provide such a process which will produce filaments in no wayimpairedwith respect to their other properties. Other objects of theinvention willbe apparent from the description given hereinafter.

The above objects are accomplished according to the present invention byextruding molten polymeric hexamethylene adipamide through a circularorifice into a quenching liquid having substantially'no solvent actionon the polymer and maintained at .atemperature of at least 35 C.Preferably, theiquenching liquid is water and, for practicaloperationpitwould be kept at a temperature of 35F-4Q" C. The filament issubsequently cold-drawn after being thoroughly soaked in water or manybe cold-drawn at a temperature somewhat above room temperature.

It has been observed that, if polymeric hexamethylene adipamidefilaments are quenched in water or the like maintained at a relativelylow temperature in order that the difference between the temperature ofthe extruded filament and that of the water may be very great, theresulting filament is, to a greater or lesser degree, fiat, that is.ellipsoidal. This deviation in the cross section of the filament fromcircular is frequently highly objectionable. Peculiarly, this difficultyis not encountered inthe manufacture of certain of the synthetic linearcondensation polymers; in fact. polymeric hexamethylene adipamide may beunique in this respect.

The present invention resides in the discovery that, if extrudedfilaments of polymeric hexamethylene adipamide are quenched in anon-solvent quenching liquid maintained at a temperature of 35 C. ormore, the cross sectional shape of the extruded filament is not changedbut retains the shape of the orifice through which the molten polymerwas extruded. This is especially observable in the manufacture ofcoarser filaments and it is the manufacture of such filaments to whichthe present invention is most advantageously applicable. Because of thisdiscovery, the manufacture of a filament of substantially circular crosssection can be assured by extruding the molten polymeric hexamethyleneadipamide through a circular orifice into a quenching liquid held at atemperature of at lcast 35 C.

Since the use of such temperature for quenching adds somewhat to thedifficulty of the usual subsequent operation of cold-drawing, thefilament thus quenched is preferably soaked in water before beingcold-drawn, or is cold-drawn while at a temperature somewhat above roomtemperature, either of which techniques facilitates the cold-drawing.

Soaking for about 24 hours in water at room temperature is ordinarilysuffieient to overcome any difliculty in cold-drawing but theallowanceof a longer time, such as two days, does no harm and may be preferablein commercial practice to ensure thorough contact of water with theinner layers of a large spool of filament and a longer period of soakingmay be required in the cerned, it is preferred that the temperature ofthe quenching liquid should not exceed 45 C.

The efiectiveness of the procedure of the pres-.-

ent invention is readily illustrated by extruding polymerichexamethylene adipamide filaments into water as the quenching liquid atvarious temperatures.

eterat a rate of 315 feet per minute into a quenching bath of water at adistance of 3.5? from the orifice. Sufiicient filament was .ex trudedwith the quenching liquid held at various temperatures to permit of thecarrying out of Molten polymeric 'hex'amethylene adipamide, of meltviscosity 700 poises, was extruded through a circular orifice of 0.060diam ten polymer should be extruded into the quench- ;ing' liquidwithout any prolonged cooling of the extruded polymer intervening. Thatis, the

of the cross sectional shape of the filament increased as thetemperature of the quenching liquid was decreased from about 35 C. Onthe other hand, it is clearly shown that filaments quenched attemperatures from 35 C. upward uniformly exhibit a deviation fromcircularity so slight as to be hardly greater than the ex perlmentalerror of the measurements (1. e. 0.00025" in 0.018", or 1.4%). I

It is not preferred to exceed a temperature of 45 C. for the quenchingliquid because the filaments quenched above that temperature become moredifiicult to cold-draw while no advantage accrues from the use of highertemperatures. Also, there may be a certain falling off of variousdesirable physical properties of cold-drawn filaments quenched attemperatures above 45 C. such .as the tensile strength of the filamentsand their recovery, 1. e., extent of 20.

their ability to straighten after having been severely bent.

In' out the present invention the molpolymer may be molten when itcontacts the quenching liquid or may be set or partially set subsequentoperationsunder commercial conditions. Specimens of filaments thusproduced were drawn by hand, i. e., stretched by'hand until they ceasedto yield, without any intermediate treatment. Filaments quenchedin thequenching liquid maintained at 40 C. or less 7 could be drawnsatisfactorily in this manner.

Other specimens of the filaments thus pro; duced were soaked in water.at C. 017.24 hours and then cold-drawnunder uniform conditions ofcommercial mechanical equipm'e' The percentage of elongationimposedfupon ea'ch filament was about 260%, i. e., every l00 feet wasdue to the preliminary cooling action of the air but the temperature ofthe polymer should not be materially below the melting point of thepolymer. Thus, in the case of polymeric hexamethylene adipamide, whichhas a melting point (in the absence of oxygen) of'about 263 C., it isdesirable that the temperature of the polymer be above'about 245C. as itenters the quenching drawn to 360 feet. Difiiculty was encountered indrawing the filament specimens quenched at 40 C. and higher. By soaking48 hours, filament specimens quenched at temperatures up to 60 C. couldbe satisfactorily cold-drawn and, by increasing the soaking another 24hours, the

filament specimens quenched at 70 C. could be Temperature Time of soak-Deviation of quenching ing before from liquid drawing circularity 0.Days Percent 12 l 31. 6 20 l 21. 1 25 l 12. 8 i0 1 7. 2 l 1. 9 l) 1. 7)40) 2) 2. 9) 2 1. 4 2 1. 4 70) 2) l. 3) 70) 3) I. 6) 80) 2) 2. 4) 80) 3)l. 9)

From this table it is apparent that flatness chlorinated hydrocarbons.

ing. Water meets these requirements and, in

addition, is readily available and has a high specific heat. It' is,therefore, the preferred quenching medium. However, a large variety ofother liquids may be employed such asalcohols, ketones, ethers. esters,hydrocarbons, and

The quenching liquid may consist of a mixture of compounds. Also, it maycontain wetting agents, dyes, and the like.

It i optional whether the quenching liquid is used in the form of a bathor a spray although the former is apt to be more convenient. Thetemperature of the liquid may be regulated or kept constant by anysuitable means.

After the filament has been quenched, the colddrawing is facilitated byfirst soaking the filament in water, the duration of said soaking beingregulated to avoid any difiiculty in, the cold drawing. Usually a periodof 24 hours will be suificient but, as shown hereinbefore, a soaking of48 hours or even longer maybe desirable where the filament has beenquenched in a liquid maintained at a relatively high temperature. Ratherthan soaking the filament in water, it may be warmed to a temperature offrom about 50 C.

toabout C. to facilitate cold-drawing.

The present invention provides a method of ensuring'thesubstantiahcircularity of cross sections of filaments of polymerichexamethylene extruded from a circular orifice and is of great practicalvalue in the production of filaments of this material for uses in whichcircularity of the filament is of prime importance. This circularity oithe filament is achieved in accordance with this invention at somesacrifice of tensile strength but without significant impairment of theother important properties of the filament.

As many apparently widely diflerent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. Process of manufacturing filaments of polymeric hexamethyleneadipamide of circular cross section, which comprises extruding moltenpolymer through a circular orifice into a quenching liquid havingsubstantially no solvent action on said polymer and maintained at atemperature of 35 C. to 45 C.

2. Process of manufacturing filaments of polymeric hexamethylene'adipamide of circular cross section, which comprises extruding moltenpolymer through a circular orifice into water main tained at atemperature of 35 C. to 45 C.

3. Process of manufacturing filaments or pclymeric hexamethyleneadipamide circular cross section, which comprises extruding moltenpolymer through a circular orifice into water maintained at atemperature of C. to (3., thereafter soaking the filaments thus formedin Water, and thereafter cold-drawing said filaments.

4. Process of manufacturing filaments of polymeric hexamethyleneadipamide of circular cross section, which comprises extruding moltenpolymer through a circular orifice into water maintained at atemperature of 35 C. to 45 0., thereafter soaking the filaments thusformed in water at about 20 C. for at least 24 hours, and thereaftercold-drawing said filaments.

5. Process of manufacturing filaments of polymeric hexamethyleneadipamide of circular cross section; which comprises extruding moltenpolymer through a circular orifice into water maintained at atemperature of 35 C. to 45 0., thereafter heating the filaments thusformed to a temperature of C. to (2., and drawing said filaments whileat approximately said temperature. v

JOHANNES ALFTHAN.

